In a conventional system for pneumatically conveying dry bulk solids such as plastic pellets or a powder, a butterfly-type valve such as that shown in FIG. 10 of the present application has previously been used. While systems utilizing this conventional type of valve have been adequate for their intended purposes, they have not been satisfactory in all respects.
In particular, due in part to frictional engagement between various parts of the valve, the valve tends to wear very quickly and rapidly loses its ability to produce an acceptable level of airtight seal. Obviously, a dependable seal which is substantially airtight is essential to efficient operation of a pneumatic conveying system. In practice, it has been found that, when a conventional butterfly-type valve of the type shown in FIG. 10 is utilized in a system for pneumatically conveying dry bulk solids such as plastic pellets or a powder, it is necessary to repair or replace either the valve itself or certain relatively expensive components thereof at relatively frequent intervals of only about three weeks under normal industrial use. Further, the structure of the conventional valve is such that, even where only repairs are needed, it is often necessary to disassemble the system sufficiently to permit removal of the valve in order to facilitate the repairs, which obviously can involve significant time and effort.
It is thus an object of the present invention to provide a valve which can be used in a system for pneumatically conveying dry bulk solids and which will require little or no maintenance.
A further object is to provide such a valve which will reliably provide an effective airtight seal each time it closes with minimal degradation over long periods of use.
A further object is to provide such a valve in which components requiring occasional maintenance can be repaired or replaced without necessarily disassembling part of the overall system and removing the valve from the system.